1. Let ƒ : R → R where ƒ(x) = x², c = -1, and u = 2. Use the e-d definition to prove Lu=? (you need to find Lu in your scratchwork).

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
Section: Chapter Questions
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Real Analysis II Please find related sample as guide to solve above problem
1. Let \( f : \mathbb{R} \rightarrow \mathbb{R} \) where \( f(x) = x^2 \), \( c = -1 \), and \( u = 2 \). Use the \( \epsilon \)-\( \delta \) definition to prove \( L_u = ? \) (you need to find \( L_u \) in your scratchwork).
Transcribed Image Text:1. Let \( f : \mathbb{R} \rightarrow \mathbb{R} \) where \( f(x) = x^2 \), \( c = -1 \), and \( u = 2 \). Use the \( \epsilon \)-\( \delta \) definition to prove \( L_u = ? \) (you need to find \( L_u \) in your scratchwork).
**Example:**

Let \( f: \mathbb{R}^2 \to \mathbb{R}^2 \) be defined as \( f(x, y) = \left( x^2 y, (3x + 2)y \right) \). Consider vectors \( u = (1, 0) \) and \( c = (1, 1) \).

**Claim:** \( Lu = (2, 3) \)

**Proof:**

Fix \(\epsilon > 0\). Choose \(\delta = \frac{\epsilon}{2}\). Assume \(0 < |t| < \delta\). Then:

\[
\frac{1}{t} \left[ f(c + tu) - f(c) - Lu \right] = \left \lVert \frac{1}{t} \left[ f(1+t, 1) - (1, 5) - (2, 3) \right] \right \rVert
\]

\[
= \left \lVert \frac{1}{t} \left[ ((1+t)^2, 3(1+t)+2) - (1, 5) \right] - (2, 3) \right \rVert
\]

\[
= \left \lVert \frac{1}{t} \left[ (1 + 2t + t^2, 3t + 5) - (1, 5) \right] - (2, 3) \right \rVert 
\]

\[
= \left \lVert \frac{1}{t} \left[ (2t + t^2, 3t) - (2, 3) \right] \right \rVert 
\]

\[
= \left \lVert \frac{1}{t} \left[ (t^2, 0) \right] \right \rVert 
\]

\[
= \left \lVert (t, 0) \right \rVert = |t| < \delta = \epsilon
\]

**Why is \( Lu = (2, 3) \)?**

\[
L = \begin{bmatrix} 
\frac{\partial f_1}{\partial x} & \frac{\partial f_1}{\partial y} \\
Transcribed Image Text:**Example:** Let \( f: \mathbb{R}^2 \to \mathbb{R}^2 \) be defined as \( f(x, y) = \left( x^2 y, (3x + 2)y \right) \). Consider vectors \( u = (1, 0) \) and \( c = (1, 1) \). **Claim:** \( Lu = (2, 3) \) **Proof:** Fix \(\epsilon > 0\). Choose \(\delta = \frac{\epsilon}{2}\). Assume \(0 < |t| < \delta\). Then: \[ \frac{1}{t} \left[ f(c + tu) - f(c) - Lu \right] = \left \lVert \frac{1}{t} \left[ f(1+t, 1) - (1, 5) - (2, 3) \right] \right \rVert \] \[ = \left \lVert \frac{1}{t} \left[ ((1+t)^2, 3(1+t)+2) - (1, 5) \right] - (2, 3) \right \rVert \] \[ = \left \lVert \frac{1}{t} \left[ (1 + 2t + t^2, 3t + 5) - (1, 5) \right] - (2, 3) \right \rVert \] \[ = \left \lVert \frac{1}{t} \left[ (2t + t^2, 3t) - (2, 3) \right] \right \rVert \] \[ = \left \lVert \frac{1}{t} \left[ (t^2, 0) \right] \right \rVert \] \[ = \left \lVert (t, 0) \right \rVert = |t| < \delta = \epsilon \] **Why is \( Lu = (2, 3) \)?** \[ L = \begin{bmatrix} \frac{\partial f_1}{\partial x} & \frac{\partial f_1}{\partial y} \\
Expert Solution
Step 1

Given that f:  where fx=x2, c=-1, and u=2

We have to find the value of Lu and prove it using ε-δ definition.

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